CVE-2026-4975: Tenda AC15 Buffer Overflow Vulnerability

CVE-2026-4975 Overview

A stack-based buffer overflow vulnerability has been discovered in the Tenda AC15 router firmware version 15.03.05.19. This vulnerability affects the formSetCfm function within the /goform/setcfm POST Request Handler component. An attacker can exploit this flaw by manipulating the funcpara1 argument, leading to a stack-based buffer overflow condition that can be triggered remotely.

Critical Impact

Remote attackers with low privileges can exploit this stack-based buffer overflow to potentially achieve code execution on vulnerable Tenda AC15 routers, compromising network infrastructure and enabling further attacks on connected devices.

Affected Products

• Tenda AC15 Router Firmware version 15.03.05.19
• Devices running the vulnerable /goform/setcfm endpoint
• Networks with exposed Tenda AC15 management interfaces

Discovery Timeline

• 2026-03-27 - CVE-2026-4975 published to NVD
• 2026-03-30 - Last updated in NVD database

Technical Details for CVE-2026-4975

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the formSetCfm function, which handles POST requests to the /goform/setcfm endpoint on the Tenda AC15 router. When processing the funcpara1 parameter, the function fails to properly validate input length before copying data to a fixed-size stack buffer.

The vulnerability can be exploited remotely over the network with low authentication requirements. Once exploited, an attacker could potentially achieve high impact on confidentiality, integrity, and availability of the affected device. This makes it particularly dangerous in network environments where the router's administrative interface is accessible.

Root Cause

The root cause of this vulnerability is improper bounds checking in the formSetCfm function. When the function receives a POST request with the funcpara1 argument, it copies the user-supplied data to a stack-allocated buffer without verifying that the input length does not exceed the buffer's capacity. This classic buffer overflow pattern allows attackers to overwrite adjacent stack memory, including return addresses and saved registers.

Attack Vector

The attack is initiated remotely via the network by sending a specially crafted POST request to the /goform/setcfm endpoint. The attacker must include a malformed funcpara1 parameter containing more data than the target buffer can accommodate. By carefully controlling the overflow payload, an attacker may be able to:

1. Overwrite the function's return address to redirect execution flow
2. Inject and execute arbitrary shellcode on the router
3. Crash the device causing a denial of service condition

The exploit has been publicly disclosed, increasing the risk of widespread exploitation. Technical details are available through the Notion Security Document and VulDB entry.

Detection Methods for CVE-2026-4975

Indicators of Compromise

• Unusual POST requests to /goform/setcfm with abnormally large funcpara1 parameter values
• Router crashes or unexpected reboots without administrative action
• Unexpected outbound connections originating from the router
• Modified router configuration or firmware without authorized changes

Detection Strategies

• Implement network monitoring to detect HTTP POST requests to /goform/setcfm with payload sizes exceeding normal operational parameters
• Deploy intrusion detection signatures to identify buffer overflow patterns targeting Tenda AC15 devices
• Monitor router logs for repeated authentication attempts or unusual access patterns to the web management interface
• Use SentinelOne Singularity platform to detect anomalous behavior on network infrastructure devices

Monitoring Recommendations

• Enable verbose logging on the Tenda AC15 device if available
• Implement network segmentation to isolate router management interfaces from general network traffic
• Deploy network-based intrusion detection systems (NIDS) at network boundaries
• Regularly audit network traffic for suspicious patterns targeting IoT and network infrastructure devices

How to Mitigate CVE-2026-4975

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management features if not required
• Implement strong access control lists (ACLs) to limit who can access the /goform/ endpoints
• Consider placing vulnerable devices behind a firewall with strict ingress filtering

Patch Information

At the time of publication, no official patch from Tenda has been confirmed for this vulnerability. Organizations should monitor the Tenda Official Website for firmware updates addressing this issue. In the absence of an official fix, implementing the recommended workarounds is critical to reduce exposure.

Workarounds

• Disable the web management interface entirely and manage the device through alternative methods if available
• Use firewall rules to block external access to ports serving the router's administrative interface
• Implement network segmentation to prevent direct access to vulnerable endpoints from untrusted networks
• Consider replacing affected devices with alternative hardware that receives timely security updates

# Example firewall rule to block external access to Tenda management interface
# Adjust the interface and IP ranges according to your network configuration
iptables -A INPUT -i eth0 -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -i eth0 -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP